Microwave amplifier



Dec. 16, 1952 F. LUDl MICROWAVE AMPLIFIER Filed Feb. 14, 1952 ATTORNEYS.

Patented Dec. 16, 1952 UNlllEZ-D STATES PATENT OFFICE 2,622,155MioRovvAvn sni'rirrinii- Tatellwlglf Pat entverwertungs-,. & Elektro-Holding A.-G., Glarus, Switzerland ApplicationFbi-iiai'y 14, 1952.Serial @527 1359'? In" switzenma February 16, 1951" This inventionrelates tom icrowave amplifiers, and particularly to amplifiers forelectric oscil-.

lations in the'range of the shorter decimeter and centimeter waves; v, W

Prior microwave amplifiers have been ofnthe traveling-wave tubetype,,or, of the velocity-j modulated beam or Klystronf type. The loadmust be adjusted to the output characteristic of a traveling-wave tubewithin definite limits to avoid a disturbing back-coupling between theamplifier output and input, and variationsiinfthe load impedance mayseriously afiect theefliciency or rate of amplification. In amplifiersoperating on the Klystron principle,an electron beam is Velocitymodulated in a'resonator or rhumbatron by the oscillations to beLamplifiedand at a certain distance beyond the resonator where theelectrons are more or le ss bunched, the beam energizes a secondresonator 'from' which the amplified oscillations'may be withdrawn. Thebunching of the electrons may b' improved by locating additionalresonators of theflsameor similar type between the inputjfand"outputreso nators, the additional'resonators'beng energized by theelectron beam to os cillate" f reelyat n *u l frequencies which satisfycertain conditions; Each resonator can impose but-onebunchingoramplifying action upon" the b'ea nfaird'the res nators must bespac'edapart by a suifri e tance to develop the focussing of th"'beam v Objectsof the'invention' are to prpvme micro;

wave amplifiers in which an el ctron bani-tr e s.

along a plurality of resonators, eac 'li res'onator interactinga'plurality of times withfthe'bearni the first resonator beingenergize'dby'th'e cl'sc'illa tions to be amplified; 'an'd *theamplified 'erierg'y'being abstracted. from -the last resonator; Ob

jects are to provide microwave amplifiersof' the character stated inwhich theresonators have" natural frequencies ofoscillationequaliatleast approximately to the frequencyof the'micro'-'slot into a pluralityof pairs of. interleaved seg ments supported inalternation from opposite" side walls of the box; and'in whichtheelernerits Fig. 2 is a through the Fig. 2a; s. a Quite. sea. chewinthe. magni tude of the highrfrequency' voltage .between'adjacentresonator segment'sflas a. function .of the posi ionof, the segmentsin.the resonator;

,Fi n3' isa. perspective. View, withsome parts.

broken; aways of. a microwave, amplifier embodying the invention the'magnet being omitted for clarity of illustration;

Fig. 4 is anend view oithe amplifier;

,Fig. 5 is an endelevationof another embodiment of the inventionin whichthe electron beam trav l l ng a urved p th; i

Fig; 5.15 a .f ragmentary perspective view of a high inductance type ofguide electrode;

Fig. '7 is a fragmentary perspective View, partly insection, ofanalternative coupling to an input or output resonator; and 7 v Fig. 8is a schematic perspectivelof apair of coupled resonators for use in awide band amplifier.

lls shownin 1 and 2, the resonator. el-

merits of thearnplifier are elongated boxes R. of

a nonrnagnetic metaland of rectangular cross-i section with one longwall divided ,by azigzag slotfA into a plurality of pairs ofinterleavedsegments f 5; of identical rectangulariorm, the segmfents beingsupported in alternationfrom opposite side walls ofthe resonator. Except'for .the end resonatorslofaa plurality or. series incorporate-dinanamplifier, which end elements mustbe provided with openings for theintroduction of input and. outputcoupling elements,

the zigza'g slot A. constitutes the. only opening cooperating with a rowof resonators 'include'a' guide electrode extending-along andfacing'theslotted faces of thelresonatorsga cathode an'd acollecting j electrode;adjacent the 'input' end and output end, respectively, oithe resonatorsfor establishing an electron 1 beam ,ingthe space between the resonatorsand the;guideelectrodef.

and a magnet orfelectromagnet; tor; establishing" a unidirectionalmagnetic field transverse to the in the wallsuof the resonator elements.The directionof .the" magnetic alternating field tabfishedWithin .aresonatorof the amplifier is indieated'inFig; Zby'the double-ended arrowH, .and..the ilvariatio'nxin the magnitude of the high-frequencypotehtialbetween adjacent resonator segments with their "position in theresona tor is shown graphically by curveU of Fig. 2a.

n" a constructional embodiment of the 'mv'ejns tion, as shown inFi'g.'3, a series of three resonators R1, R2 and R3 are spaced from eachother the reso-.

by small gaps F1, F2 and secured to a rail or strap G of nonmagneticmaterial which supports them within an evacuated envelope D. Thesegmental walls of the several resonators face and are parallel to aguide electrode L of strap or band form which extends along and projectssomewhat beyond the ends of the resonator assembly. A cathode K isarranged transversely of the guide electrode L, and in part within asemicylindrical depression of the electrode L, at substantially theouter end of the resonator R1 into which extends an input loop I withleads P1 for connection to the source of microwaves to be amplified. Thecathode K and a collector electrode C at the opposite end of the tubeestablish an electron beam in the interspace between the segmental facesof resonators and the guide electrode -L. One or more additionalcathodes K1 may be provided along the guide electrode L to increase themagnitude of the beam current towards the output end of the resonatorseries in accordance with the increase in oscillation energy. Aplurality of cathodes is particularly advantageous when the amplifier isto deliver considerable power. The terminal resonator R3 of the seriesis provided with a coupling element, not shown, having leads P2 forconnection to the antenna or other load device upon which the amplifiedmicrowave energy is to be impressed.

A unidirectional magnetic field is developed in the space between theresonator segments and the guide electrode, and in the directionindicated by the arrows N of Fig. 3, by a permanent magnet or otherelectromagnetic system M, Fig. 4.

The method of operation of an amplifying tube of the construction so fardescribed is as follows. The collecting electrode C and the resonatorsare maintained at a positive direct current potential with respect tothe cathode K by any appropriate current source, not shown, and theguide electrode L is maintained at the same, or approximately the same,potential as the cathode. These relative potentials will of courseresult in an electron beam to the collector electrode C when the cathodeK is heated to liberate electrons, and the electrons move on cycloidalorbits in view of the magnetic field in the direction N. So long as theinput resonator R1 is not energized by a high frequency input injectedby loop I, the electron beam will be substantially homogeneous or of thesame density at all transverse cross-sections.

Upon energizing the input resonator R1 byimpressing the oscillations tobe amplified across the input leads P1, the alternating magnetic field Hestablished within the resonator develops an alternating potentialdifference U between adjacent segments S1 and S2 of the resonator; allsegments S1 being instantaneously of the polarity opposite that of thegroup of segments S2, and the polarity of the segments reversing at thefrequency of the oscillations to be amplified. The alternatingpotentials thus developed on the resonator segments exert a focussingeffect upon the electron beam and the electrons leave the range of theresonator R1 in packets or bunches which succeed each other at thefrequency of the oscillations to be amplified. The bunching of theelectrons is very marked, particularly in the vicinity of the exit endof the resonator, as the initial bunching effected by the firstresonator segments interacts with the later segments to increase theexcitation of the resonator and the magnitude of the potentialdifferences between adjacent resonator segments as initially establishedby the microwave energy introduced into the resonator at the loop I. Therepeated interactions between the electron beam and the resonatorsegments distinguish the invention from the known amplifiers in whicheach resonator imposes only a single bunching action upon the electronbeam. It is to be noted that the length, and hence the number ofsegments, of a resonator can not be increased indefinitely as theresonator will breakinto self-oscillation if too many reactive couplingsare provided.

The bunched electron stream leaving the range of the first resonator R1reacts with the initial segments of the next resonator R2 to energizethe same, and is further focussed and more compactly bunched by theinteraction of the resonator segments and the electron beam. Similarly,the resonator R3 is energized by the bunched electronstream leaving thesecond resonator, and the amplified oscillations are abstracted from theoutput resonator by a loop and the leads P2.

A special advantage of the described amplifier is the absence of areactive coupling between the output and input resonators. The amplifieris therefore stable in operation and is not materially affected by widevariations in the frequency and/or impedance of the load into which itworks. When connected to a transmitting antenna, for example, itsstability is not affected by hoarfrost or ice which collects on theantenna and changes its electrical characteristics. The amplifier istherefore particularly suitable for the amplification of frequencymodulated oscillations where it is difficult to maintain a closematching of the amplifier output characteristics and the loadcharacteristics over the frequency range of the transmitted signals. 7

The linear arrangement of the resonator series and guide electrode isnot essential for operation in accordance with the invention and it maybe more convenient, for manufacturing or other reasons, to employ acylindrical construction such as shown in Fig. 5. Except that theseveral elements are arcuate in place of linear, they correspond exactlyto elements shown in Fig. 3 and are identified by primed referencecharacters but will not be described in detail. The opposed surfaces ofthe resonator elements and the guide electrode G are coaxial to providea beam path of constant cross-section from end to end thereof.

The band type of guide electrode shown in Figs. 3 and 5 usually affordsonly a negligible back-coupling of the output resonator to the inputresonator and even this back-coupling is suppressed by a guide electrodeL1 in the form of a flattened spiral winding of wire, with slightlyspaced adjacent turns, Fig. 6, which has a very high impedance at thefrequency of the oscillations to be amplified.

In place of the loop couplings to and from the resonators, a pair ofinput or output leads P may be connected directly to two segments S1 andS2 of a resonator, as shown in Fig. 7.

The several resonators of Figs. 3 and 5 are designed and constructed toresonate at substantially the frequency of the oscillations to beamplified. When the amplifier is to operate over a relatively wide rangeof frequencies, each resonator element of the amplifier comprises tworesonators R and R. in series in the row of resonator elements andcoupled electrically or magnetically as indicated by a jumper J, Fig. 8;the resonators of each pair being tuned to somewhat differentfrequencies, for example to frequencies (f+a: and (,fa:) as indicated bysuch notations on the respective resonators.

It is to be understood that the invention is not limited to theparticular embodiments herein shown and described as variousmodifications thereof fall within the spirit and scope of the inventionas set forth in the following claims.

I claim:

1. A microwave amplifier comprising an evacuated envelope to be locatedin a unidirectional magnetic field, cathode means and a collectorelectrode within said envelope and spaced from each other to develop anelectron beam, a plurality of resonator elements extending in spaceddecoupled sequence along the path of the electron beam, each resonatorelement comprising an elongated metal box having a natural frequency ofoscillation at least approximately coinciding with a frequency of themicrowave oscillations to be amplified and having the wall thereofopposed to the electron beam divided by a zigzag slot into a pluralityof pairs of interleaved segments which extend transversely to the pathof the electron beam, input and output coupling means extending into theresonator elements respectively most remote from and closest to saidcollector electrode, and a guide electrode extending along the path ofthe electron beam at the side thereof opposite said resonator elements;said amplifier being adapted to be energized by maintaining saidcollector electrode and resonator elements at positive potentials withrespect to said cathode means and said guide electrode, and establishinga unidirectional magnetic field through the interspace between saidresonator elements and said guide electrode parallel to the resonatorelement segments.

2. A microwave amplifier as recited in claim 1, wherein the guideelectrode and the surface defined by the opposed segmental walls of theresonator elements are substantially linear and parallel.

3. A microwave amplifier as recited in claim 1, wherein the guideelectrode and the surface defined by the opposed segmental walls of theresonator elements are cylindrical and substantially coaxial.

4. A microwave amplifier as recited in claim 1, wherein said guideelectrode is of strip form.

5. A microwave amplifier as recited in claim 1, wherein said guideelectrode comprises a flattened spiral winding of spaced turns of wire.

6. A microwave amplifier as recited in claim 1, wherein said cathodemeans comprises a plurality of spaced cathodes, one cathode beinglocated adjacent the outer end of the resonator element most remote fromsaid collector electrode.

'7. A microwave amplifier as recited in claim 1, and for operation overa band of frequencies, wherein each resonator element comprises a pairof coupled resonators in series arrangement along the path of theelectron beam, the resonators of each pair having natural frequencies ofoscillation respectively above and below the mean frequency of said bandof frequencies.

FRITZ LtiDI.

No references cited.

